Electrical and electronic applications require the use of capacitors in many circuits for power, control and conversion. Frequently, these capacitors must have great capability in both storage capacity and voltage. Film capacitors in particular have been used in many applications where a high storage capacity is desirable, such as in electric power generation and conversion. Frequently, many of these capacitors are employed in parallel in order to gain a multiplication of capacitance.
These capacitors can fail, sometimes bursting their seams and causing secondary damage. If a capacitor fails shorted, its normal failure mode, it generates gases and creates pressure inside the body of the capacitor. This causes the body of capacitor to bulge. If no relief is provided, generally in the form of an internal disconnect, the capacitor may even explode.
For these and other reasons, it is desirable to remove a failed capacitor from an electrical circuit as soon as possible after it has failed, preferably instantaneously. This problem has received attention from a number of sources over the years.
In several prior approaches to solving this problem, a capacitor is placed inside a housing, while the electrical terminals of the capacitor remain outside the housing. In one such method, electrical wires connect the capacitor to the terminals, and when the capacitor bulges, the wire is physically broken. In others, a fusible link or spring is used to break the connection. These solutions are less than optimal, because the hardware used for connecting and mounting, as well as the failed capacitor itself, are often damaged. They cannot be reused and must be replaced. These approaches are catalogued in U.S. Pat. Nos. 3,304,473, 4,106,068 4,754,361, 4,897,760 and 5,019,934.
U.S. Pat. No. 4,812,941 discloses a film capacitor wherein the end portion will physically lift off the internal contacts when it fails in this fashion. This method interrupts the circuit. However, the operation requires a far more elaborate construction than the capacitor itself, and this entire expensive structure is rendered useless upon failure. There is no possibility of reusing any of the deformed or broken internal components.
U.S. Pat. No. 5,222,899 features a repetitively useful contactor, spring driven and with a manual reset, which would be far too bulky for operation with capacitors used for smaller electrical circuits. Even with these devices, pressure inside a film capacitor can quickly build up, bulge outwardly, and without other intervention, relieve itself explosively, damaging itself and other hardware in the immediate vicinity.